1. Field of the Invention
The present invention relates to directional wave detector apparatus for determining, with the help of the directin of movement of the travelling waves passing a measuring point in a power supply network, which may also comprise cables, the direction to the fault that has caused the travelling waves, and more particularly to such apparatus for determining whether the fault lies within or outside the range of protection of the relay protection device which comprises the wave detector.
2. Prior Art
When a fault occurs in a power supply network it leads to travelling waves moving along the line. It is known to use the direction of movement of such travelling waves at a measuring point to determine the direction to the location of the fault. As an example of this, reference is made to U.S. Pat. Nos. 3,878,460 and 3,956,671. A fault which occurs within the range of a power line supervised by a relay, is called a fault lying ahead. In the travelling waves which from such a fault move inwardly towards the measuring point of the relay, the current and voltage waves have different signs so that the relationship u=-Z.sub.o .multidot.i is obtained, where the voltage is designated u, the current i and the wave impedance Z.sub.o. If the fault appears in the opposite direction from the location of measuring, the relay senses that the voltage and current waves have the same sign and the above-mentioned relationship is changed to u=Z.sub.o .multidot.i. The relay then interprets the fault as a fault lying behind the measuring point.
The travelling waves which from the location of the fault move along the power line, comprise transients within a wide frequency range. It is known to filter out the stationary component of the fundamental frequency by band exclusion filters, so that only changes are sensed, and then compare the signs of the voltage and current waves, and with the guidance of the result of that comparison determine the direction to the location of fault. It is also known to exclude the filtering and compare the voltage and current waves directly.